A Direct and Functional Interaction Between G _o and Rab5 During G Protein–Coupled Receptor Signaling

Abstract

Rab5 is a small guanosine triphosphatase (GTPase) that regulates the early stages of endocytosis and is conserved in eukaryotes. Rab5 regulates the internalization of receptors and other membrane-associated signaling proteins. The function of Rab5 in these processes is considered relatively passive, so that the endocytic capacity of Rab5 is used during, for example, beta-arrestin-dependent internalization of G protein (heterotrimeric guanine nucleotide-binding protein)-coupled receptors (GPCRs). Direct recruitment or activation of Rab5 by the components of these signaling pathways has not been reported. Here, we demonstrate an interaction of Drosophila Rab5 and an immediate transducer of GPCR signaling, the G protein G(o), in vitro and in vivo. Rab5 and G(o) bound to each other as purified proteins, as well as in fly extracts. In cellular assays, G(o) led to Rab5 activation and endosome fusion. We further showed that the G(o)-Rab5 interaction functioned in Drosophila planar cell polarity and Wingless signal transduction, pathways initiated by GPCRs of the Frizzled (Fz) family. Additionally, the recycling Rab GTPases Rab4 and Rab11 functioned in Fz- and G(o)-mediated signaling to favor planar cell polarity over canonical Wingless signaling. The interplay between heterotrimeric G proteins and Rab GTPases controlled receptor internalization, revealing a previously uncharacterized regulatory mechanism in GPCR signaling.

Outside-in signaling – a brief review of GPCR signaling with a focus on the Drosophila GPCR family

“…The role of the atypical GPCRs of the Frizzled family in establishing segment polarity through the Wnt signaling pathway has been well characterized. Frizzled family members can also act as canonical GPCRs by signaling through Gα(o) (Katanaev et al, 2005), which in turn recruits Rab5, an important regulator of endocytosis, to the plasma membrane (Purvanov et al, 2010). Endocytosis and morphogenesis are tightly linked, so this link between Gα(o) and Rab5 has potentially important implications for embryonic development.…”

Wnt/beta-Catenin Signaling and Small Molecule Inhibitors

“…One of the Go subunits, G o, uses an RGS domain to interact directly with Axin, recruiting it to the membrane [54,228]. G o also interacts with Rab5, an interaction that presumuably promotes the internalization of the Wnt/Frizzled/LRP complexes [54,229]. The Go subunit, G , recruits Dishevelled to the plasma membrane upon Wnt binding to the Frizzled receptors [54].…”

Yellow submarine of the Wnt/Frizzled signaling: Submerging from the G protein harbor to the targets

“…It has been proposed that different ways to package Wnts serve to activate different groups of cells in the natural environment, depending on the location of these cells regarding the source of production of the Wnt morphogens [61,62]. It is conceivable that different subtypes of the intracellular signaling pathways are activated by different forms of Wnts, and circumstantial evidence exists in favor of this idea [63][64][65]. LRP5/6, capable of interacting with lipoprotein particles, might play different roles in the recognition of the different forms of Wnt ligands and initiation of different subtypes of signaling.…”

“…In the canonical b-catenin-dependent signaling, internalization of Fz was proposed to enhance the initial signal emanating from the plasma membrane [65,135,136]. In the PCP branch of the pathway, Fz is endocytosed and transported along microtubules to be released at the apical posterior membrane to elicit planar polarization of the epithelia [81].…”